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Is the water safe to drink?


Yes. The taste and odor is a palatability issue. The palatability change that results from a naturally occurring algal bloom does not alter the quality of the water provided to the cities and the communities served. The water supply remains safe for use with no health risks created by these events.


What causes the taste and odor changes?


A natural occurrence in all surface water supplies, an “algal bloom” is responsible for the taste and odor changes in the treated drinking water supply. Algal blooms usually occur in Lavon Lake in late July and into August each year, but can occur at any time if the right conditions exist in the water supply reservoir.


Summer Algal Blooms
As hot temperatures remain prevalent, ideal conditions are set for an “algal bloom.” Summer algal blooms occur when high temperatures warm the reservoirs, little or no rainfall has occurred, and sunlight penetrates the water allowing photosynthesis to occur. When these conditions are present, the blue green algae species Nostoc and Anabaena will reproduce or “bloom”.


Winter Algal Blooms
The mid-summer “algal bloom” is the most common; however, infrequently a winter algal bloom can create taste and odor changes in the water supply during cooler weather patterns. When winter algal blooms occur, an earthy or metallic taste and/or odor might be noticeable in the water supply.


What steps does the NTMWD take to control the taste and odor?


Currently, NTMWD laboratory personnel perform algal counts to confirm the occurrence of an algal bloom and the algal species which are responsible for the changes in taste and odor. During an algal bloom, laboratory analysis of raw water samples can show high levels of geosmin. Geosmin and MIB (2-Methylisoborneol) are produced by an algal bloom, but geosmin is more predominant in the winter and MIB in the summer. Geosmin and MIB are organic compounds released during the decomposition of algal species. Utilizing current treatment processes, the NTMWD can reduce but not eliminate the taste and odor issues.


The NTMWD has implemented the use of ozonation which is expected to significantly reduce and/or eliminate taste and odor issues caused by algal blooms. Previous studies and thorough testing have shown that the use of ozone, an oxidation process, to supplement the current treatment process can provide additional advantages including: micro-flocculation to reduce chemical usage, micro-constituent oxidation, and taste and odor control.


While no taste and odor control process is 100% effective, ozonation will eliminate or greatly minimize the palatability issue of the water supply. The NTMWD and consultants will continue to analyze the potential causes of taste and odor episodes, the source of heightened levels of geosmin, and additional methods to address the issue.


What are the conditions for an algal bloom to occur in Lavon Lake?


  • Nutrients must be present – such as nitrogen, phosphorus and calcium, which are derived from decaying vegetation in the lake.
  • Turbidity has lessened – the turbidity or cloudiness of the lake water has cleared up, allowing the penetration of the sunlight. This occurs due to lack of rainfall.
  • Temperature increase – the optimum temperature range of the lake water for an algal bloom to occur is between 80° - 85°. This is provided through many hot summer days.


When all conditions are met, photosynthesis will take place and the algae will grow and/or proliferate. Algal species, such as anabaena, secrete an “oily” substance from their cells that causes an odor in the water supply. Aquatic fungi, actinomycetes, grow on dead and decaying algae and cause an earthy taste in the water.